The present invention relates generally to a process for casting lead grids for electric battery plates, and in particular, to an improved mold for use in casting such lead grids, and the corresponding manufacturing process.
Battery grids, especially those used in starter batteries, are often manufactured in two-part hinged casting molds which receive a molten lead flow (lead melt) either by gravity, or under pressure. To reduce adhesion of the lead melt to the mold (which is usually formed of cast iron), to permit air to escape from the mold cavity (particularly during gravity casting), and to counteract excessively rapid cooling of the lead melt, such molds (particularly those used for gravity casting) are conventially provided with a thin powder layer made of cork-flour or talc which is progressively consumed as the mold is used (generally after a life corresponding to, at most, 5000 castings). Consequently, this thin powder layer must eventually be renewed, and only after a time-consuming cleaning operation. In the case of die-casting, the molds are provided with a parting layer made, for example, of beef suet. This is performed before each casting.
A major improvement to this process is disclosed in EP-PS No. 65,996, which calls for the original metal casting mold to be lined with temperature-resistant ceramic molding plates. These plates are interchangeable, and are especially favorable for the fine, thin webs of starter grids because of the dimensional stability of the ceramic material.
However, practice has shown that due to its porosity, the conventional cork-flour layer is substantially more permeable to the air which is displaced by the casting process than are the known ceramic inserts. Additionally, due to the relatively low thermal insulation of known ceramic linings as compared to the coated (cork-flour layer) metal molds, practice has shown that heat is too rapidly dissipated from the lead melt, and that this heat dissipation is not sufficiently differentiated by the canals which are traditionally provided in the mold to receive a cooling medium.